Like TCP, BGP is connection-oriented. An inexplicit unification between digit BGP speakers is ingrained before some routing aggregation is exchanged. This unification takes locate on protocol opening 179. As with EIGRP and OSPF, keepalive messages are dispatched conceive by the BGP speakers in meet to ready this relation alive.
Once the unification is established, the BGP speakers mercantilism routes and aline their tables. After this initial exchange, a BGP utterer module exclusive beam boost updates upon a modify in the meshwork topology.
The IGP protocols that ingest Autonomous Systems, IGRP and EIGRP, order likely neighbors to be in the aforementioned AS. This is not genuine with BGP. Routers crapper be in assorted Autonomous Systems and ease mercantilism routes. The BGP neighbors do not hit to be direct connected, and ofttimes are not, but do requirement to be healthy to accomplish the IP addresses they ingest in their edge statements.
A BGP person that is in the aforementioned AS is referred to as an Internal BGP (iBGP) Peer, where a BGP person in added AS is an External BGP (eBGP) Peer.
A distribution iBGP configuration:
Router bgp 100
Neighbor 10.1.1.2 remote-as 100
A distribution eBGP configuration:
Router bgp 100
Neighbor 10.1.1.2 remote-as 200
Cisco recommends that eBGP peers be direct connected, where iBGP peers mostly module not be.
Before we intend likewise such far into BGP theory, lets intend a plan started. Youll ingest the router bgp bidding to configure a router as a BGP speaker. Right after that, the edge bidding module be utilised to refer this BGP speakers possibleness neighbors. (The cost peer and eighbor are reciprocal in BGP, but it's the edge evidence that is utilised to statically delimitate neighbors. BGP is not confident of discovering neighbors dynamically.)
R1(config-router)#neighbor 172.12.123.3 remote-as 200
While nearly every of the edge options are meet that -- nonmandatory -- you do hit to take the BGP AS of the far router. BGP has no execution to dynamically conceive neighbors. Remember, BGP speakers do not hit to be in the aforementioned AS to embellish peers. To avow that the far BGP utterer has embellish a peer, separate exhibit ip bgp neighbor.
R1#show ip bgp neighbor
BGP edge is 172.12.123.3, far AS 200, outside link
BGP edition 4, far router ID 0.0.0.0
BGP land = Active
Last feature 00:01:39, stop instance is 180, keepalive quantity is 60 seconds
Received 0 messages, 0 notifications, 0 in queue
Sent 0 messages, 0 notifications, 0 in queue
Route change request: conventional 0, dispatched 0
Default peak instance between advertizing runs is 30 seconds
The production here crapper be a lowercase dishonorable the prototypal instance you feature it. The prototypal highlighted distinction shows 172.12.123.3 is a BGP neighbor, is settled in AS 200, and is an outside link, indicating that the edge is in added AS entirely. The ordinal highlighted distinction shows the BGP land as Active. This sounds great, but it actually effectuation that a BGP person unification does not still subsist with the likely neighbor.
So modify though the exhibit ip bgp edge production indicated that this is an Active edge relationship, thats not as beatific as it sounds. Of course, the think the person relation hasnt been ingrained is that we havent organized R3 yet!
R3(config)#router bgp 200
R3(config-router)#neighbor 172.12.123.1 remote-as 100
Verify the person organisation with exhibit ip bgp neighbor:
R3#show ip bgp neighbor
BGP edge is 172.12.123.1, far AS 100, outside link
BGP edition 4, far router ID 172.12.123.1
BGP land = Established, up for 00:01:18
Last feature 00:00:17, stop instance is 180, keepalive quantity is 60 seconds
Local host: 172.12.123.3, Local port: 179 (BGP uses protocol Port 179)
Foreign host: 172.12.123.1, Foreign port: 11007
The person relation between R1 and R3 has been established.
Now that you undergo how the edge relation itself is built, you crapper move acquisition the some options of the edge command. Youll hit to officer these to embellish a CCNP and CCIE, and well move hunting at those commands in the incoming conception of this BGP tutorial!
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